1,720,962 research outputs found
Modelling breakdown durations in simulation models of engine assembly lines
Full text linkMachine failure is often an important source of variability and so it is essential
to model breakdowns in manufacturing simulation models accurately. This thesis
describes the modelling of machine breakdown durations in simulation models of
engine assembly lines. To simplify the inputs to the simulation models for complex
machining and assembly lines, the Arrows classification method has been derived
to group machines with similar distributions of breakdown durations, where
the Two-Sample Cram´er-von Mises statistic and bootstrap resampling are used to
measure the similarity of two sets of data. We use finite mixture distributions fitted
to the breakdown durations data of groups of machines as the input models for
the simulation models. We evaluate the complete modelling methodology that involves
the use of the Arrows classification method and finite mixture distributions,
by analysing the outputs of the simulation models using different input distributions
for describing the machine breakdown durations. Details of the methods and
results of the grouping processes will be presented, and will be demonstrated using
examples
Evaluation of the arrows method for classification of data
No full textWe evaluate the Arrows Classification Method (ACM) for grouping objects based onthe similarity of their data. This is a new method, which aims to achieve a balancebetween the conflicting objectives of maximizing internal cohesion and external isolationin the output groups. The method is widely applicable, especially in simulation input andoutput modelling, and has previously been used for grouping machines on an assemblyline, based on data on time-to-repair; and hospital procedures, based on length-of-staydata. The similarity of the data from a pair of objects is measured using the two-sampleCram´er-von-Mises goodness of fit statistic, with bootstrapping employed to find thesignificance or p-value of the calculated statistic. The p-values coming from the pairedcomparisons serve as inputs to the ACM, and allow the objects to be classified such thatno pair of objects that are grouped together have significantly different data. In thisarticle, we give the technical details of the method and evaluate its use through testingwith specially generated samples. We will also demonstrate its practical application withtwo real example
Comparison of simulation output series using bootstrapping
No full textWe describe a method for comparing stochastic outputs of simulation models. The method is distribution-free and allows the comparison of sets of data with different numbers of data points. This makes it ideal for performing comparisons between simulation output and the real output of the system being modelled, when often there are many more data points available from the output of the simulation model than present in the real data. We calculate the two-sample Cramer-von Mises goodness-of-fit statistic between the two sets of data, using bootstrapping to find the distribution of the statistic, and so the probability that the two sets of data were drawn from the same distribution
Modeling server usage for online ticket sales
No full textThis article describes the use of a discrete event simulation model to estimate the server power required for the online sale of concert tickets to a required service standard. Data are available on the number of purchases made per hour and the percentage of tickets booked online for previous concerts and we describe how these are used to estimate the number of users in the system. We use bootstrapping to allow us to take account of the variability in this estimate when calculating the confidence intervals for the simulation model outputs. A queuing model is also introduced, which is useful to provide a quick calculation of how busy the server is before running the more computationally-intensive simulation model. A numerical example is used to describe the model and the methodology
Optimal scheduling using length-of-stay data for diverse routine procedures
No full textThe paper describes the use of length-of-stay data to derive an optimal schedule for operating theatres. We consider situations where there are a large number of types of procedures that must be scheduled. The general approach we describe is to classify procedures by their length-of-stay data. An efficient scheduling tool can then be used to determine the optimal schedule for operations, where the aim is to reduce variability in the number of beds being used. We describe the application
of the method using a case study coming from a network of private hospitals in the UK
Classification analysis for simulation of the duration of machine breakdowns
No full textMachine failure can have a significant impact on the throughput of manufacturing systems, therefore accuratemodelling of breakdowns in manufacturing simulation models is essential. Finite mixture distributions havebeen successfully used by Ford Motor Company to model machine breakdown durations in simulation modelsof engine assembly lines. These models can be very complex, with a large number of machines. To simplifythe modelling we propose a method of grouping machines with similar distributions of breakdown durations,which we call the Arrows Classification Method, where the Two-Sample Cram´er-von-Mises statistic is usedto measure the similarity of two sets of the data. We evaluate the classification procedure by comparing thethroughput of a simulation model when run with mixture models fitted to individual machine breakdowndurations; mixture models fitted to group breakdown durations; and raw data. Details of the methods andresults of the classification will be presented, and demonstrated using an exampl
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
